The present invention relates to a control apparatus for controlling the operation of an outboard marine engine. More particularly, it relates to such an engine control apparatus which is effective to prevent a reduction in propulsion force due to cavitation (under unloaded or idling operation) caused by bubbles produced by a propulsion screw, thereby providing for improved acceleration performance.
FIG. 3 schematically illustrates a typical example of an outboard marine engine mounted on a boat at a location outside a boat hull. In this figure, the engine 1 in the form of an internal combustion engine for outboard use is disposed outside a boat hull 3 at the stern thereof and mounted to the boat hull 3 through a mounting member 1a. A propulsion screw 2 is disposed under water and operatively connected with the engine 1 so that it is thereby driven to rotate.
FIG. 4 shows in block form the general construction of a conventional engine control apparatus for controlling the outboard engine 1 of FIG. 3. In this figure, a rotational speed sensor 4 is mounted on a camshaft or crankshaft (not illustrated) of the engine 1 so that it generates a crank signal representative of a reference crankshaft position in synchronization with the rotation of the unillustrated crankshaft for sensing the rotational speed or the number of revolutions per minutes of the engine 1 and generating a corresponding output signal R. A throttle sensor 5 senses the throttle opening or the degree of opening of a throttle valve (not shown) of the engine 1 corresponding to the quantity of depression of an unillustrated accelerator pedal of the engine 1 by an operator, and generates a corresponding throttle signal .alpha.. A controller 6 receives output signals from various sensors indicative of various engine operating conditions including the output signals R, .alpha. of the rotational speed sensor 4 and the throttle sensor 5, and generates a drive signal A for controlling various engine control parameters on the basis of these output signals. An actuator means 7 is operatively connected to the controller 6 so that it is driven to operate by means of the drive signal A from the controller 6. The actuator means 7 controls various driving and control elements or devices such as a fuel pump, an ignition coil, a throttle actuator or motor, a starter motor and the like associated with the engine 1.
Next, the operation of the above-described conventional engine control apparatus will be described in detail while referring to FIGS. 3 and 4. First, the controller 6 generates a drive signal A based on the output signals from the various sensors including the rotational speed signal R, the throttle signal .alpha., the reference crank signal and the like representative of various engine operating conditions, for controlling the actuator means 7 (e.g., for controlling a fuel pump, an ignition coil, a throttle valve, etc.) as well as calculating and controlling operational timings thereof such as fuel supply or injection timing, ignition timing, etc. In addition, the controller 6 also determines, in response to the gear position of an unillustrated transmission, a proper degree of throttle opening .alpha. so that the flow rate of intake air sucked into the engine 1 is thereby properly adjusted to provide a desired number of revolutions per minute of the engine 1.
Here, it should be noted that in the case of the marine engine 1 for outboard use, the propulsion screw 2 entrains or draws in air at the time of engine starting or acceleration, so there develop a great deal of bubbles around the screw 2. In particular, such a tendency becomes remarkable when the engine in operation is moved or pivoted about the mounting member 1a in a direction (i.e., in the counterclockwise direction in FIG. 3) designated by an arrow.
If a great amount of bubbles are produced by the screw 2, the thrust or propulsion force thereof would be accordingly reduced under the influence of resultant cavitation (i.e., unloaded operation), thus resulting in that a desired acceleration could not be obtained. In order to avoid this situation, the controller 6 generates an appropriate drive signal A so as to suppress an abrupt increase in the rotational speed of the engine 1 at all times irrespective of the presence or absence of bubbles around the screw 2. This inevitably reduces the maximum acceleration performance of the engine 1.